Multiple radio transmission system



Nov. 18, 1941. M. l. HULL 2,262,764

MULTIPLE RADIO TRANSMISSION SYSTEM Filed July 18, 1958 9 Sheets-Sheet 1 i"- tz,

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MULTIPLE RADIO TRANSMISSION SYSTEM Filed July 18, 1938 9 SheeIs-Sheet 2 glvwc/wfom MAURY I. HULL FIG-.2.

Nov. 18, 1941. M. l. HULL 2,262,764

MULTIPLE RADIO TRANSMISSION SYSTEM Filed July 18, 1938 9 Sheets-Sheet 5 i a!) Elma/who'l E MAURY HULL Nov. 18, 1941.

M. l. HULL 2,262,764

7 MULTIPLE RADIO TRANSMISSION SYSTEM Filed July 18, 1938 9 Sheets-Sheet 5 I Q 9 LL \& K i Q @Q 2 E vv I Qwumvbom M. l. HULL MULTIPLE RADIO TRANSMISSiON SYSTEM Now/.18, 1941.

9 Sheets-Sheet 6 Filed July 18, 1938 MAURY' HULL.

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MULTIPLE RADIO TRANSMISSION SYSTEM Filed July 18, 1938 9 Sheets-Sheet 7 :1 it Q Q 0' h 2 &

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MULTIPLE RADIO TRANSMISSION SYSTEM Filed July 18, 1958 9 Sheets-Sheet 9 FIG. l4

MAURY 1. HULL Patented Nov. 18, 1941 UNITED I STAT ES: PAT ENT FF I CE 2,262,764. MULTIPLE RADIO TRANSMISSION SYSTEM Maury. 1. Hull, Washington, 1). o.

Application July 18,1938, Serial No. 219,785

(Granted under the act of March 3,1883, as.

amended April 30, 1928; 370 0. G. 757) 16 Claims.

This invention relates to signalling systems and more particularly to systems for transmitting and receiving a plurality of signals simultaneously.

An object of the invention is to provide a system in which a plurality of signals may be transmitted on a single carrier wave. 7

With this object in view my invention contemplates an arrangement in which alternate cycles or groups of cycles of a carrier frequency are modulated by signals from two separate'sources, the rate of alternation being above audibility.

The invention may be adapted to the transmission and reception of more than two messages simultaneously.

Further objects of my invention are to provide in a wave transmission system a novel means whereby a voltage bearing sub-harmonic relationship to a carrier frequency is used to insure that alternate cycles or groups of cycles of the carrier wave are modulated by separate intelligence and in a receiver to provide novel means whereby a voltage bearing a sub-harmonic relationship to the received carrier is used to insure that the carrier modulated at the transmitter in the fashion described above is so broken up in the receiver in synchronism with the incoming signals that the two or moredntelligences are properly separated and received.

Other and further objects of the invention will be apparent from the following specification when read in connection with the accompanying drawings in which: 7

Figure 1 isa circuit diagram of a preferred form of transmitting circuit and arrangement for accomplishing the purposes of the invention.

Figures 2, 3, and 4 are circuit diagrams showing modifications of the transmitting system shown in Figure 1.

Figure 5 is a diagrammatical showing of a circuit arrangement which may be used as a modification of both the transmitting circuit of Figure 1 and the receiving circuit of Figure 8.

Figure 6 is a circuit diagram showing the transmitter of Figure 1 in another modified convenient desired frequency. It is preferably a piezo electric crystal control vacuum tube oscillator but it may take any of several known forms. The output from the source of oscillations S. O. is connected to the input circuit of a radio frequency amplifier shown as a rectangle designatedR. F. A. The radio frequency amplifier R. F. A. is preferably of the vacuum tube type with a resonant plate circuit load, but it may be any one of many well known amplifier circuits. The output of the radio frequency amplifier R. F. A. is connected to the input circuit of a phase shifter shown as a rectangle'designated P. S. The output of thephase shifter P. S.

is connected to the primary of the radio fre- The secondary 2 of the radio frequency transformer |-2 is center.

quency transformer l2.

tapped. The end terminals of the secondary 2 are connected to the control grids of the Vacuum tubes 3 and 4 respectively. The center tap connection of the secondary 2 is connected to one terminal of a source of biasing potential '5, the other terminal of which is connected to the cathodes of tubes 3 and 4. A source of anode or plate potentialis shown at 6, one terminal being connected to the cathodes of the tubes 3 and 4 while the other terminal is connected to the anodes of tubes 3 and 4 via the resistances 1 and 8 respectively. The anodes of tubes 3 and 4 are connected via sources of biasing potential 9 and I0 respectively tothe control electrodes of vacuum tubes 13 and [4 respectively. The mid point between resistances l and 8 is connected to the cathodes of tubes I 3 and I4 by way of the secondary 1'2 of a radio frequency transformer ll l2. The primary ll of the transformer Il-.-l2 is energized indirectly by the source of oscillations S. O. in the following manner, namely:

The source of oscillations S. O. has its output connected to the input circuit of a frequency multiplier or frequency doubler, the rectangle designated F. D. The output of. the frequency multiplier or frequency doubler F. D. is connected to the input circuit of a variable attenuator, the rectangle designated V. A. The output of the variable attenuator V. A. is connected to the primary H of the transformer HI2. Microphones or other sources of signals are shown at H] and 20 connected via amplifiers l1 and I8 respectively to the primaries of audio frequency transformers l5 and I6 respectively. One end of the secondary of the audio frequency transformer 15 is connected to the anode of the tube l3 while the other end is connected to a source of anode potential 21 by way of the resistance 23., One

end of the secondary of the audio frequency transformer I 6 is likewise connected to the anof the anode batteries 21 and 28 are connected togetherto the cathodes of the tubes l3 and I4. Radio frequency by-pass condensers 43 and 44- are connected across the secondaries of audio frequency transformers I and lt'respectively.

The point in the anode circuit of tube l3 be;- tween the secondary of transformer I5 and the resistance 23 is connected to one terminal of a coupling condenser 3|,C the other terminal of which'is. connectedto the control electrode of tube 2|. The point in the ano'dexcircuit of tube I4 between the secondary of transformer l6 and the resistance 24 is connected-to oneterminal of acouplin'g condenser .32, the other terminal of which is connected to. the control electrode of- Batteries 29 and 30 supply biasing potube 22. tentials for the control; electrodes of tubes 2| and 22 respectively byway of resistances 25 and 26 respectively. f

The plates or. anodes of the tubes 2| and 22 are connected" together to .one end of the coupling resistor '33, the other end of which is con nected to one terminal of a sourceof potential or battery 35,"the other terminal of which is connected'to the, cathodes of thesetubes.

The anodesof thetubes 2| and 22 are connected to one terminal of a coupling condenser 31, theother terminal of which is connected to thecontrol electrode of the tube 38.. .Biasing potential is, supplied to the control electrode of the tube 38 from the sourceof potential 36 by,

bias for the grids of these tubes so that with no voltage applied to the transformer l2 no plate current would flow in the plate circuits of tubes 3' and 4. Then during that part of the cycle of the incoming frequency to transformer 1-2 which induces a positive potential on that terminal of the secondary 2 which is connected to the grid or control electrode of the tube 3, the

' grid ofjthis tube will be made less negative with respect to its filament and current will flow in its plate circuit. At the same instant the other secondary terminal of inductance 2 will be negative,,so that the grid of the tube 4 will be made more negative; and no current will flow in the the transformer lil2 will cyclically change'the potential of the grids or control electrodes of tubes I3 and I4 tendingto make the grids less negative with respect to. their. respective 'cathodes Orfilaments (I shall refer to this hereafter as the positive alternation or positive half cycle from inductance I 2). Current will flow simultaneously in the'plate circuits of both tubes 13 and I4. On the next half cycleof the radio frequency voltage applied to .the transformer 1il 'l2,'the grids of the tubes l3 and 14 will tend to become more negative. and since these tubes arealready normally biased to cut-off any instantaneous increasein negative .grid voltage doesnot influence theYanode circuits. If the voltagehis continuously introduced via trans former ll"l2fthere will be a series of pulsations of plate Tcurrent at the radio frequency in the plate circuits of tubes I3 and I4. These pulsations in this casewill occur simultaneously in the output circuit's'of tubes l3 and I4 during the positive half of a. cycle of the voltage intro 'duced in secondaryl2. Assuming nowthat tubes 3 and 4 are in operation and; that thebattery" 5 supplies suff cient plate circuit of tube, 4 since this tube is normally biased to cut-off by the voltage of battery 5, and hence the instantaneous increase in negativeggrid-voltage does not affect the plate circuit of tube 4. During the next half cycle of the incoming; voltage introducedin the secondary 2 the potentials across thetwo terminals are re versed and plate current flows in the plate of tube 4 butnotin'that of tube; 3. This type of amplifieris familiarly known as a push-pull a p fi r;

,The .currentsflowing in; theplate circuits of tubes 3 and 4 cause potential differences across their respective loadresistances 1 and 8 which in tum cause instantaneous increases; in the negative grid potentials of tubes l3-and -l4, such instantaneous increases in ;the negative grid potentials of tubes,l3--and I 4- being equal to the product of the instantaneous plate currents in amperesmultiplied by the respective values of plate resistances I and 8-in ohms. The operation above described maybe more readily understood by reference to thecurve shown in Figure-.10 wherein the instantaneous grid voltages on tubes 13 and I4 are shown-Whenboth transformers l-'-2v and -H- -I2 are being excited by voltages oftheproper frequency, amplitudes and phasal relationship. In Fig. 10 the upper section A shows the individual voltages operating in the input circuit of tube l3, and the lower section B shows the individual voltages operating in the input section of tube 14. In section A curve I is the steady negative component of bias supplied by the battery 9 curve II is the voltageintroducedat {2; curve III represents the voltage dropacross resistance 1 occurring on alternatealternations transform l2.. In section .B? curve I is they steady negative biasing potential supplied bythe battery [0; curve II is the voltage introduced at l2 and is in the same phase. as that of curve II of section A; curveII is 'the'voltage'drop across resistance 8 occurring on alternate alternations of the input voltage to transformer l2, and is oppositeinphase to'the voltage change across resistance I. Assuming that the frequency multiplierv F; D. doublesthe frequency, and assuming that the" attenuator V. A. and the radio frequency-amplifier R. A. are. relatively adjusted so that the voltages introduced at the secondary 'l2 and those developed by the potential'difierences across resistances 1 and 8 for relative amplitudes as shown in Figure 10, and assuming that the phase shifter P. S. is adjusted so that zero and degrees of the lower incoming frequency from secondary 2 coincides on the time axis with 270 degreesof the higher incoming frequency from; the secondary l2, then it.

will be seen that theposltivealternations or positive half'cycles ofthe incoming radio frequency of-fthe' inputvoltage to voltage from the secondary I2 produce plate current pulsations in alternate'tubes of the two tubes I3 and I4. If the'positive alternation of the first cycle of the incoming voltage from the secondary I2 produces a flow of current in tube I3, then it does not produce a flow of current. in tube I4. The corresponding alternation of the next cycle of voltage from secondary I2 will then produce a flow of plate current in tube I4, but not in tube I3. During the positive alternations or positive half cycles of the voltage introduced at secondary I2, tube I3 will have a plate current pulsation during, say, half of cycles I, 3, 5, 1, etc., while tube I4 will have plate current pulsations during the corresponding half of cycles 2, 4, 6, 8, etc. This is brought about by the potential difference developed across resistances I and 8 as may be seen by referring to Figure 10. Curve III as mentioned before illustrates the instantaneous voltages developed across resistances I and 8 due to plate current flowing in tubes 3 and 4. These voltages are of such polarity as would tend to make the grids in tubes I3 and I4 negative with respect to their filaments. are in a push-pull arrangement, their plates draw current alternately'and hence alternate voltage rises shown by curve III affect alternate tubes of the group I3 and I4. Curve II illus- Since tubes 3 and 4 trates the voltage introduced at secondary I2 which is twice the frequency of that introduced at secondary 2. Due to the circuit arrangement, voltages induced in secondary I2 act simultaneously and similarly on both tubes I3 and I4,

so that by referring to Figure 10 itis seen that while the first positive alternation shown in curve II would activate both tubes I3 and I4, the corresponding negative voltage rise in curve III at the same instant effects only one of the tubes I3 and I4, offsetting the positive voltage of curve II for that particular tube but not for the other which has aplate current pulsation due to its grid potential becoming less negative for an instant. Now proceeding to the second positive alternation of'curve II this time the negative voltage rise shown in curve III counteracts the effects of the voltage shown in curve II on a different tube of the group I3-I4, so that the tube of the group I 3I4 active before is now idle, while the tube idle before is now active. The process thus continues as long the excitation of radio frequency transformer I-2 and II-IZ continues with the proper frequency and proper phase and magnitude.

These two sets of pulsations in the plate circults of tubes I3 and I4 are modulated in the plate circuits of their respective tubes by the modulating transformers I5 and I6, which vary the plate voltages of tubes I3 and I4 and hence vary the magnitude of the radio frequency pulsatio'ns in their plate circuits in conformance with the frequency and magnitude of the voice or other signals introduced at microphones I9 and respectively, and amplified by tubes I1 and I8 respectively.

The curves shown in Figure 9 depict the manner in which the outputs of tubes 2I and 22 modulated by two different intelligence frequencies and combined in the load impedance 33. In Figure 9 the load currents in load resistance 33 are plotted against time. The pulsations B were supplied by, say, tube I3 and are varied in amplitude in accordance with the modulations envelope A supplied by the audio frequency transformer I5. Pulsations D were supplied by tube I4 and are variedi'n amplitude in accordance with the modulation envelope C supplied by the audio frequency transformer I6. A, B, C, and D below thef'zero pointcorrespond ,to those above, and represent those portions'of the emitted wave supplied by the fly wheel effect-of inductance 40, and which were not present in the resistance loadat 33. I l

The functions of tubes 2| and 22 in Figure 1 are to combine both sets of pulsations 1mm load impedance after they have been separately modulated. These tubes are ordinarily biased by batteries 29 and 30 so that they function as linear amplifiers having a non-inductivedoad, furnished by the resistance 33. In the plate-circuit of tube 38 'radio frequency 'transf'ormer 40-4I, connected to the antenna, supplies the other half of the radio frequency cycle; f 1

The description of the operation'of the transmitter given above as illustrated by Figures 9 and 10, has been based upon the assumption that the frequency applied to the frequency-exciting transformer II-I2 is twice that applied to the' transformer I-2. Assuming, however, that the frequency multiplier designated F. D. generates a frequency four times that of the source which activates the transformer I2, it is obvious that instead of alternate cycles of the carrier" being modulated by the two signals, now alternate groups of cycles would be divertedto alternate amplifier tubes and so modulated, each group containing two cycles. Instead of employing a frequency multiplier or frequency doubler F. D. between the sourcesof oscillations S. O. andthe' 1 variable attenuator V. A. a sub-harmonic generator may be inserted between the source of oscillations S. O. and the radio frequency amplifier R. F. A. supplying radio frequency to the phase shifter P. S. and thence to'the radio fre quency transformer I--2 In the above descriptions of the operation of the transmitter, the two tubes I3 and I4 have been modulated by transformers I5 and I6 in their respective plate circuits. It'is contemplated that the present invention includes a system in which these tubes are modulated in their grid circuits also as shown in Figure 2.

In Figure 2 the same reference characters are used as in Figure 1 to denote like parts and certain of the apparatus has been omitted from the drawings, it being understood, however, that the input circuits of tubes 3 anal and the transformer II'-I2 are energized in the same-man neras in Figure 1. The circuit of Figure 2 differs from that of Figure 1 in that theinodulating transformers I5 and I6 and their by-pass condensers have been moved from the plate circuit of tubes I3 and I4 and placed in the grid circuits of the respective tubes. The amplifiers including tubes 2I22 and 38 of Figure 1 havebeen eliminated from the modification shown in Figure 2 and the plates of tubes I3 and I I aresupplied with potential from a single source 21" via the primary 40 of the radio frequency transformer 4Il-4I', whereinthe outputs of tubes I3 and I4 are combined and coupled 'tothe antenna systern. The operation of the system shown in Figure 2 is substantially the same as that described in connection with Figure 1, but with the following differences: In Figure 2 the 0scillat-ions impressed upon tubes I3 and I4 are modulated in the input circuit to these tubes and the output modulated oscillations :frorn'tubes I3 and III are combined directly in 'the'pri' nary 40 of the radio frequency transformer.

-Where tubes .I3-and I 4 (Figure2);ar.emodu lated in their grid circuits, the combination of voltages as illustrated in Figure 10 must be modified somewhat by the'addition of a fourth voltage which is introduced into the circuit as a result of audiofrequency transformers l5 and I6. For convenience in analyzing the action of the fcircuit, it may be thought of as affecting only the amplitude of the positive portionof the altema- .tions of curve II. The peaks of curve III will now have to develop sufficient negative amplitude to-offset the positive alternations of curve II; plus: the value of the positive alternations of voltages introduced at transformers l5 and I6.

In the case of plate modulation of tubes l3 and l4 as in Figure 1, curve III has to be of sufiicient negative amplitude to offset only the positive amplitude of curve II.

Figure v3 shows another modification of the transmitter circuit of Figure 1. In this modification, the outputsxof tubes [3 and I4, which now 'have a common plate battery. 28', are modulated in their plate circuits as in Figure 1, but

the outputs of these tubes are directly. coupled to the input of tubes 2|; and 22 respectively,

whose outputs are"combined directly-in the load inductance; Battery supplies the grid bias voltage to both tubes 2| and 22-. Batteries f and 35" supply the plate potential for tubes 2| I .and22v through radio frequency choke coils and respectively. Coupling condensers 4! and 48 connect the'plates of tubes 2| and 22, to, inductance-40, allowing the radio frequency currents to pass. while offering a practicallyinfinite impedance to direct current. Condensers 49 and 50 complete the respective output ;circuits of 'tubes2l and 22. The condensers 49 and 50 should have a high reactance to the radio frequency used compared to'the resistances 23 and 24 in the input circuits of tubes 2| and 22 re spectively. i

Theoperation of the system shown in' Figure I '3 is similar to the operation described above in connection with Figure 1.

1 and 8. These circuit elements or appropriate combinationsof any of them may be coupled to;

the plate circuits of tubes l3 and I4 instead of to their grid circuits in such manner as to divide the carrier voltage into alternate cycles or groups of cycles which may have been modulated or may be subsequently modulated by separate intelligences. Such a circuit arrangement is shown in Figure 4.

In Figure 4 the secondaries of the modulation transformers l5 and I6 shunted by radio frequency by-pass condensers are connected to the respective control grids of tubes l3 and I4. The other ends of the secondaries are connected together andto the cathodes of tubes l3 and I4 by way of the secondary l2 of the radio frequency transformer lll2 and the source of biasing potential In. The platesof tubes l3 and I4 are supplied with energizing potential from the source 28 by way of coupling'resistors 1-23 and 8-24 respectively. The plates of tub'es l3 and I4 are connected respectively to coupling condensers 3| and 32 which are in turn connected to the control grids of tubes 2| and 22 respectively as shown and described in connection bodiment the outputs of 'tubes'3 and 4 are applied to the plate circuits of tubes'l3 and 14 respectively. The plate of tube 3 is connected'to that point in the plate circuit of tube I3 between the coupling resistors I and 23. The plate of tube 4 is connected to that vpoint in the -plate y circuit of tube l4 between the coupling resistors 8 and 24. Plate potential is supplied to the plates of tubes 3 and 4 frombatteryfi connected to the filaments thereof by the connection extending from the battery 6 to the juncture between coupling resistors I and 8 and thence through these resistors to the respective tubes 3 and 4.

In this arrangement voltages'are alternately developed across resistances 1 and 8 of such polarity that they oppose the positive voltages introduced at battery 28, and hence render tubes I3 and I 4, alternately inoperative, by reducing their plate voltages to zero or'less (negative). As a result tubes 13 and [4 will alternately supply excitation to the amplifier comprising tubes 2| and 22 provided thevoltages introduced in the secondary I2 of transformer |l l2 and that existent across resistances 1 and 8 are in the proper phasal and magnituderelations as before, and the operation of the circuit of Figure 4 will,

I as in Figure 1, provide for the finaltransmitt'er I and 19 are connected directly to the outermost,

. grid tubes.

carrier being alternately modulated by two intelligences via tubes 13 and I4 which are separately modulated in their grid circuits.

Figure 5 shows a modification of the trans mitting circuit of Figure 1 for the use of double Tubes 18 and 19 correspond to tubes 3 and 4 of Figure l. The plates of tubes 18 grids of double grid' tubes 86 and 8'! respectively. Plate potential is supplied to the plates of tubes 18 and 19 fromthe source of potential 80 via the coupling resistors 8| and 82. In Figure 5 the tubes 86 and 81, correspond to tubes l3 and I 4 in Figure 1. The grids nearest to the oathodes. or filaments in tubes 86 and 81 are'connected tog-ether to the cathodes or filaments of these same tubes via the secondary. 84 of the radio frequency transformer 83-84 and a source of grid biasing potential 85. The plates of tubes 86 and 8! are connected respectively to the secondaries of modulation transformers 88 and 89 respectively which correspond to transformers l5 and I6 of Figure 1 respectively. The remainder of the circuit of Figure 5 (not shown) is substantially like that shown in connection with Figure l. The operation of Figure 5 is substan tially similar to the operation of Figure 1 except that instead of the voltages from the secondary 84 to the transformer 83-84 (the transformer corresponding to transformer ll--l2 in Figure 1) and the voltages from the resistors 8l-82 (coupling resistors corresponding to resistors I and 8 in Figure 1) being combined in one circuit they each operate to change the potentials on respective grids of tubes 86 and 81, so that as before negative potentials developed across the resistors operate on alternate tubes of the pair 8681 to counteract positive potentials from the secondary 84, by means of ingences in the. same. manner: as transformers. and I6 in Figure 1. I

Figure 6 showsv a'modification of thegtransmitting circuits of Figures 1 and: 5' using triple. grid tubes. In this circuit triple grid tubes I3- and I4 correspond to tubes I3 and I4 respectively in Figure 1 and 86 and 81 respectively in Figure 5.- The connections in Figure 6 are. substantially identical with those of Figure 5 with the excepa tion that the modulation transformers I5: and it have their secondaries connected between the cathode or filaments and the intermediate grids of the respective tubes I3 and, I4. In thisara rangement the varying potentials derivedv from the modulation transformers I5 and Itmodulate the respective outputs of the tubes I3 and I4; in accordance with the individual intelligences impressed thereon. v s

In Figures 5 and 6 it is understood that the arrangement of the order of the grids can .be changed, for instance in Figure 5 the grid of the tube 86 which is nearest to the filament could be, connected to the plate-of the tubes-I8 and vice versa. Likewise in Figure 6 any desirable ar-. rangement of the grids could be used. It is to be further understood that in Figures -5 and 6 the various grids of the tubes are to be biased to the appropriate desired potentials.

Figure 7 shows an adaptation of the transmitting circuit of Figure 1 for the transmission of four intelligences simultaneously. As will be seen it comprises in part two similar circuits, each similar to that portion ofthe circuit of Figure 1 included between the transformer I2 and the pair of tubes 2I and 22 inclusive. Inaddition, in Figure 7 there is a push-pull amplifier including radio frequency. transformer 5I5Z, amplifier tubes 53 and 54, a source of biasing potential 55 for biasing the grids of said tubes, a

source of anode potential 56 and tube load reg sistances 51 and 58 connected in the respective plate circuits of tubes 53 and 54. The plate load resistance 5'! and 58 are connected in series with the secondaries I2 of the transformers I.I--I2 in the input circuits of tubes I3 and I4 of. the respective upper and lower similar portions of thecircuit of Figure 7 corresponding generally to Figure 1. Withthe resistances 51 and 58 each connected in series with one of the secondaries I2 of one of the, two duplicate radio frequency transformers ,I II2, plate current flow in tubes 53 and 54' via resistances 5! and 58 respectively causes a potential diiference to be developed thereacross which serves to increase instantane- I ously the negative grid potentials of the duplicate, input circuits associated with the two transformer secondaries I2. A flow of current in resist-. ance 57 tends to producea negative potentialon the grids of tubes I3 and I4 ,in the upper portion of the diagram. A flow of current in resistance 58 tends to produce a negative potential on the grids of the tubes I3 and I4 in the lowerportion of the diagram. In Figure 7 a second frequency doubler or frequency multiplier ED. is. utilized and a second phase shifter P.,S. is employed-so that the phasal relationship of the currents in the transformers 5I52, I-2, and II--I2 can be adjusted with respect to eachother. v

The operation of the circuitof Figure 7 is best understood by referencev to the curve of Figure 11. Assuming first that the radio frequency transformer 5I-52 is energized by a voltage offrequency f, both radio frequency. transformers I-2 by a frequency 21, and both radio frequency transformers II'I2 by. a frequency 4f. which be comes the carrier frequency, all of the proper relative magnitude and phasal relationship with respect to each other, which may be obtained by the frequency doubler F. D. and the phase shifter P. S., together with'the amplifier R. F. A. and variable attenuator V. A. In Fig. 11 the individual voltages operating in the control circuits of tubes I3, I4, upper and lower sections. are shown. Section A shows the individual voltages active in the input or control circuit of upper tube I3. Section B shows the individual voltages active in the input circuit of upper tube I4. Section C shows the individual voltages active in the input circuit of lower tube I3. Section D shows the individual voltages active in the input circuit of lower tube I4 of Fig. '7. In all sections (A, B, C, and D) I is the bias supplied by bat teries 9 and III. In all sections the curve II represents the voltages of frequency 4 introduced at transformers I2, and are all in phase in all tubes. In Section A. III is the voltage drop across the upper resistance I; in section B the curve III represents the voltage drop across resistance 8; in section C the curve III is the voltage drop across the lower resistance I; in section D the curve III represents the voltage dropacross lower resistance 8. Voltage drops occur simultaneously in both resistances! and occur simultaneously in both resistances 8 on the opposite half of cycle of frequency 2f from that of resistance I.

In sections A and B the curve IV represents the voltage drop across resistance 5'I occurring simultaneously in the input circuits of upper tubes I3 and I4. In sections C and D the curve IV represents the voltage drop across resistance 58, or, in other words, the voltage across resistance 58, which influences the input circuits of lower tubes I3 and I4 in phase. The voltage drops in resistances 51 and 58 occur during alternate alternations of the voltage of frequency ff 7 I The operation of the entire circuit of Figure 7 is' best explained by describing the action at the four instants when the alternations of curve II are positive. t is assumed that both transform-. ersf I".2 are excited in phase and both transformers I I I2 are excited in phase. By reference to Figure ,llit is seen that at the instant of the first positive alternation of voltage in curve II, reading from, left to right, voltage I is operative in the grid circuits of all four tubes I3.I i, voltage II is operative in all four grid input circuits, and corresponding tubes of both pairs of tubes I3.-I4 are blocked by the negative potential shown in curve III. In addition, tubes I3 and M of either the lower or the upper part of the circuit of Figure 7 are further blocked by the negative potential shown in curve IV developed by a potential diiference existent across one of the resistances 51' or 58. It will be assumed for purposes of ex planation that the first voltage rise of curvev III operates on both tubes I3 and the second voltage rise of curve III operates on both tubes l4. It will also be assumed for purposes of explanation that the first negative voltage rise of curve IV operates on the upper group of tubes I3 and I4, and the second voltage rise of curve IV operates on the lower group of tubes I3 and I4. Then the first positive alternation shown in curve II produces a plate current pulsation in the lower tube I4, but in none of the others. On the second positive alternation shown in curve II, as before thevoltages shown in curves I and II are operative in all four tube input circuits. But now the voltage corresponding to that shown in curve III transformer 66-6 l.

blocks both tubes I4; the voltage corresponding to that shown in curve IV still blocks the upper tubes l3 and I4; so that on the second positive alternation of curve II only the lower tube I 3 has a plate current pulsation. Now, on the third positive alternation of the voltage corresponding to curve II both the lower tubes l3 and I4 are blocked by the negative voltage corresponding to curve IV, and the upper tube I3 is blocked by the negative voltage corresponding to curve III, so that only upper tube [4 has a plate current pulsation during the third positive alternation shown in curve II. On the fourth positive alternation of curve II both lower tubes 13 and I4 are still blocked by the voltage corresponding to that of curve IV, and the upper. tube [4 is blocked by.

the voltage corresponding to curve III, so that only the upper tube I3 has a plate current pulsation. On the fifth positive alternation of curve II' the entire cycle just described is repeated.

The output of each of the tubes l3 and I4 is separately modulated in its plate circuit, and all 11 are connected together'to the highpotential side of a source of plate potential 15, the low potential side of which is connected to the oathodes'or filaments of tubes H and 12. By-pass condensers 13 and 14 are connected across fromfour outputs are recombined in the'load impedance of resistance 33.

It is contemplated that any of the modifications of the circuit of Figure 1 may also be applied to that of Figure '1. Multi-grid tubesco-uld.

be used in this arrangement in place of tubes l3 and I 4. In a system employing four grid tubes,

one of the grids could be excited by the voltage. supplied at transformer |ll2, one grid by the voltage supplied from resistances I and 8, one. by the voltage from modulation transformers,- and one by the voltages from resistances 51 and v 58. The tubes 53-54, 3-4, etc., could be enclosed in a single envelope having a duplicate set of elements. Withthis arrangement the two grids could be separately terminated, the two 3 plates could be separately terminated, and the two filaments or cathodes could be terminated together or be a single emitting electrode.

Referring now to Figure 8 a description will be given of one form of receiving circuit for separat ing the two sets of radio frequency cycles or 1 groups of cycles to derive therefrom the two separate signals or intelligences. In Figure 8 a re- P. S. The output of the phase shifter. P. S. is

1 connected to the primary 60 of radio frequency The secondary of the transformer 60-6l is center tapped. The end terminals of the secondary 6| are connected to the 1 control grids of amplifier tubes 62 and 63, respectively. The center tap of the transformer secondary 6| is connected by means of a source of biasing potential to the cathodes or filaments of j the tubes 62 and 63. The plates 0r anodes of tubes 62 and 63 are connected by respective coui pling resistors 66 and 61 to a source of plate p0. tential 65, one terminal of which is connected to (the cathodes or filaments of tubes 62 and 63. The plates of tubes 62 and 63 are connected directly to the control grids of tubes H and 12 re- 1 spectively. The cathodes or filaments of tubes 3 1| and 12 are connected together through the secondary 10 of a radio frequency transformer 5 69-70 and a source of grid biasing potential 68 1 to a point between the coupling resistors 66 and 61. The output of the radio frequency amplifier R. F. A. is also connected to the input of a varicathode or filament to anode or plate of the respective tubes H and 12. The tubes 62 and 63 are preferably normally operated as linear amplifiers biased to cut ofi by the biasing battery 64 so that with no excitation from inductance 6| nocurrent flows in the resistances 66 and 61'.

- The two tubes II and 12 are normally biased.

to cut off by the grid bias battery 68 in their circuits. The resistances 66 and 61 are so connected that any current flowing inthem due to plate currents in tubes 62 and 63 create potential differences which increase the respective negative grid potentials on the two detector tubes H and I2.

The operation of the receiver is substantially along the following lines: The incoming wave (bearing two intelligences) is received and amplified by the radio frequency amplifier R. F. A., the output of which excites 'a frequency divider which in turn excites transformer 606l. The

operation of tubes 62-63, ll-42 is exactly simrier to the two detector tubes H and 12 where they are rectified and delivered to the load circuits 16 and 11. The rate of alternation of the received wavein the receiver is maintained in ,synchronism with that of the transmitter by using a sub-harmonic of the carrier to excite the transformer 66--6|. Any shift in frequency in the source of oscillations in the transmitter will automatically cause a like shift in the harmonic 4 and sub-harmonic frequencies used at the transmitter and receiver, so that the entire system always stays in synchronism. It is not necessary to smooth out the modulated carrier in order to obtain sine wave to excite the transformer 6ll6l in the receiver; the output of the frequency divider should contain no harmonics but maybe non-sinusoidal because as long as the voltages introduced in resistances 66 and 61 have certain minimum value, the extent of their maximum value is unimportant. Operation of the receiver for percentages of modulation approaching one hundred per cent is obtained by adjusting the relative values of voltages at transformer 606| and 6910 so that the voltages at resistances 66 and 61 will always be sufficient to properly counteract the maximum modulated peak voltages introduced by way of transformer 69-10 for any given percentage of modulation. How much further the instantaneous voltages in 66 and 61 rise above this necessary minimum is immaterial. In

certain instances where signals are modulated at high percentages, an amplitude discriminating amplifier may be inserted between the frequency divider D and the phase shifter P. S., or the subharmonic frequency may be generated locally by a crystal oscillator which may or may not be influenced by the incoming signals.

The curve shown in Figure 12 illustrates the operation of the receiving circuit of Figure 8. Pulsations of plate current F (plate current plotted against time) occur in the plate circuit of tube 'II, conforming to the modulation envelope E. Pulsations of plate current H occur in the plate circuit of tube 12 conforming to the modulation envelope G. Although both of these sets of pulsations are positive, they are drawn in different directions from the Zero axis to indicate that they are supplied by different tubes.

The current which produces the signal in indicating devices I and 11 respectively is the average value of the plate current pulsations occurring at radio frequency in the tubes II and I2. As a result of diverting alternate cycles or groups of cycles of the carrier to different detector tubes the average value of the plate current in each tube is reduced by one-half, but the shape of a modulation envelope remains the same.

It will be apparent that the circuit arrangement of Figures 4 and 5 may also be used as an adaptation of the receiving circuit of Figure 8.

In so adapting the circuit of Figure 5 the transformers 88 and 89 would be replaced by signal indicating devices I6 and I1. Transformer 83B4 would then be fed by the carrier frequency corresponding to that applied to transformer "69 in Figure 8, and tubes IS and I9 would be excited by a sub-harmonic frequency, through the center tapped transformer secondary 6 I The receiving circuit of Figure 8 may be adapted to receive four signals simultaneously transmitted from a transmitter similar to that shown in Figure '7 when the receiving circuit of Figure 8 is modified in accordance with the teachings of Figure '7, the modification of which appears to be obvious. In this case two frequencies would have I resistances 91 and to be derived from the received carrier, being onehalf and one-fourth of the carrier frequency.

Figure 13 shows a further circuit for accomplishing the purposes of the invention. All of the circuits described heretofore have used amplifiers which were activated by and amplified only one-half of the voltage of carrier frequency and which depended upon the flywheel effect of an inductance or tuned circuit to supply a voltage or current of substantially symmetrical or sinusoidal shape. In Figure 13 both halves of the voltage of carrier frequency are each symmetrically modulated. Alternations of each half are diverted to different amplitude tubes (four in all) where they are modulated so that now alternate complete cycles of the voltage of carrier frequency are modulated by individual intelligences and subsequently recombined to form one continuousradio frequency signal. This is accomplished by having a duplicate circuit to divide, amplify and modulate alternate alternations of that half of the cycle of the voltage of carrier frequency which was not affected by the circuit comprising transformer I through tubes I3 and I4 in the drawings. As was explained in the description of Figure 1, only those half cycles or alternationsof the voltage on the secondary of transformer lI-I2 which tended to make the grids of the tubes I3 and I4 positive with respect to their filaments were utilized by the circuit; those alternations of opposite polarity were not used and tubes I3 and I4 were both idle during the instants of the unused alternations mentioned above. In the circuit of Figure 13 those alternations unused before are now used to activate a duplicate-pair of amplifying tubes I03- -I04 corresponding to tubes I3 and I4", and

I03-I04 by means of a duplicate set of tubes 93 and 94 corresponding to tubes 3 and 4. The operation of this duplicate amplifying circuit comprising transformer 9I92, tubes 93 and 94, and 98 is exactly similar to its counterpart and is illustrated by the curve in Figure 14, partB. In Figure 13 the primaries I I and II of transformers II-I2 and I0 I-IOZ are excited by the same voltage oppositelyphased, so.

that the voltages introduced in secondaries I2 and I02 are oppositely phased. This determines that those alternations of voltage of frequency 2 which produce positive potential on the grids of tubes I3 and I4" will produce negative potential on the grids of tubes I03 and I04, while those alternations of voltage at the frequency zf'which produce negative potentials on the grids of tubes I3 and I4" will, produce positive potentials on the grids of tubes I03 and I04.

The operations of those portions of the circuit of Figure 13 which divert corresponding alternations of alternate cycles of voltage of frequency 2f to alternate amplifying tubes are similar to their operation in Figure 1. The rectangle 9.0 in Figure 13 is a phase shifting device for advancing or retarding the phase of the voltage of frequency f by degrees as shown by the curve in Figure 14. 1

In Fig.14 the curves at "A and B show the voltage applied to the outer grids of tubes I3" and I4", respectively, and are identical with Fig. 10. The lower portions C and D of Fig. 14 depict the combination of voltages in the outer control grid circuits of tubes I03 and I04, respectively. The curve II represents the same voltage in the lower portions C and D as in the upper portions A and B except that the alternations are reversed as to the direction of voltage change with respect to time; alternations positive in the upper portions A and B" are negative in the lower portions C' and D, and vice-versa, as explained above by the opposite phasing of the potentials applied to transformers II and IIJI. The curve III" represents the voltageintroduced by the potential differences developed across re-, sistances 91 and 98. The phase of curve 111" has been retarded 90 from that of curve IIL'so that the zero and of the voltage from curve III" will coincide with 270 of the voltage from curve II. I s The four tubes I3, I4, I03 and I34 are modulated by transformers I5 and It in accordance with the well-known system of grid modulation. Transformer I5 modulates both alternations of one cycle of the voltage of frequency 2 while transformer I6 modulates both alternations of the succeeding cycles of voltage of frequency 2 The outputs of the four tubes are combined in the primary I36 of the transformer IBIS-4|. The output of the four tubes is subsequently delivered to a load circuit connected to the secondary II, as shown in Figure 1. Although double grid tubes are shown in Figure 13 at I3", I4, I03, and I04, single grid tubes might be used where the double grid tubes are shown, and the various sets of alternations separately modulated in e t e the and or plat circuit of the various alternate alternations of this group are diverted to alternate tubes of the group f in one load circuit impedance. sible modifications of the circuit of Figure 13 are apparent, and are contemplated'as included with-'- subsequ'ently modulated before being combined Many other posin-the scope of the appended claims. The adaptations of Figure 13' may be 1 channel circuit of Figure .7.

applied to the four While in the explanations of Figures 10, 11 and 14, thevarious 1 voltages represented by curves III, III 'and III" are described as coinciding on the time axis with 1 1 zero and 270 degrees of the voltages correspond- 1 ingltocurves and II, it is not necessary that these figures be exact, but only suflicientlyclose 1 that-the various voltages have sufficient amplitude at any and allinstants to properly perform f their desired functions. Y

- It is understood that while in-the drawings batteries have been shown as a source of supply 3 of grid and plate voltages for all tubes, any other [suitable source could be used. It is also understood thatseparate sources of employed where common sources have been shown and vice versa, provided no undesirable jcoupling between the circuits is introduced thereby.

, Many other modifications of the above circuits are possible, and the drawings referred to are ,only representative and are not intended to limit the invention thereby,-nor are the descriptions to be considered as limitations. For instance, the inductive coupling of transformers l l-l 2, |-'-2, 6970, etc., could be replaced by resistance coupling. "The variable attenuators V. Arand the radio] frequency amplifiers R. F. 'A.-can" be dispensed with in certain cases where the'proper amplitude relationships of the two voltages of different frequencies are inherently attained. The phase shifter P. S. might be eliminated under certain circuit conditions. Diode rectifierscould be ,used in place of tubes 3 in place of tubes 62 and 63in Figure 8, etc. The frequencies f, 2], etc. need not be harmonically related in all cases. It is understood thatthe embodiments of my invention-are not to be restricted by ,the'foregoing specifications or by the accompanying drawings, but only by the scope of the appended claims. a

1 The above described invention may be used by dr for the Government of the United Stateswithout the payment of any royalty thereon.

Iclaim: i

1 1. A radio transmission system'for modulating correspond-ing alternations of alternate cycles of a carrier wave of frequency 2f with two separate intelligences, comprising a source tof oscillations, means for derivingfrom said source-of oscillations two frequencies, one of frequency f and one of, frequency 2f, a pair of radio frequency translators of the thermionic tube type each having at least a cathode, a control electrode and an anode, means for applying to the control electrodes of said tubes a direct current component of potential of such value that substantially no anode current flows therein in the absence of the application of other components of potential to the control electrodes of said tubes, means for impressing upon. the control electrodes of the tubes of said translators two additional components of potential of substantially the same amplitude, one component of frequency f in phase opposition in the two translators, and the potential may; be

and 4m Figure '1 and I other component of frequency ifin phase in'the two tubes, whereby anode current may flow in only one of said tubes at any instant, means for separately modulating the oscillations impressed upon the control electrodes of the tubes of the prising a source of oscillations, means for deriving from said source of oscillations, oscillations of two frequencies, one of frequency f and one of frequency nf, a pair of radio frequency translators of .the thermionic tube type each having at least a cathode, a control electrode and an anode, means for applying to the control electrodes of said tubes a direct current component of biasing-potential of such value that substantially no anode current flows therein in the absence of the application of other components of potential to the control electrodes ofsaid tubes, means for impressing upon the control electrodes of the tubes of said translators two additional components of potential of substantially the same amplitude, one component of frequency in phase opposition in thetwo translators, and the other component of frequency nf in phase in the two translators, whereby anode current may flo'w'in only one of said tubes at any instant, meansfor separately modulating the oscillations impressed upon the control electrodes of the tubes of the tWo translators of said pair, and means for combining and transmitting the I separately modulated oscillations.

3. A transmission system in accordance with claim 1 in which the oscillations of frequency 2f applied to said pair of translators are separately. modulated in the grid circuits of said translators.

4. A transmission system in accordance with t quency f by means of a frequency doubler.

5'. A radio transmission system for modulating 1 corresponding alternations of alternate cyclesof a carrier wave of frequency 2 with two separate intelligencies, comprising a source of oscillations, means for deriving from said source of oscillations two frequencies, one of frequency f and one of frequency 2), a pair of radio frequency translators of the thermionic tube type each having at least a cathode, two grid electrodes and an anode, means for applying a potential of the frequency 2 to one of the grids'of each of said tubes in phase and means for applying a potential of the frequency f in phase opposition to the 60 other of the grids of the respective tubes, the polarity and amplitude of the potentials of frequency f being-of such value as to always render one or the other of saidtubes inoperative to pass anode current. r

6. A'system as set forth in claim 1 in which the tubes of said translators have at least three grids, means for applying a potential of the frequency 2 to one of the grids of each of said tubes in phase, means for applying a potential of the frequency f to another one of the grids-of said tubes in phase opposition and means for applying to the ponents of potential from said first source to the control grids of said tubes in phase opposition in the two tubes, and means for applying components of potential from said second source to the control grids of said tubes in phase in the two tubes said components of potential applied from said second source being at least no greater in amplitude than the components applied from said first source.

8. A wave translating system in accordance with claim 7 in which said tubes each include a second control grid and means for applying to each of said second control grids an individual signal potential for modulating the waves translated by each of said tubes with the signals individual thereto.

9. A wave transmission system comprising a source of alternating current potential, a pair of thermionic tubes each having at least a cathode, a control grid and an anode, means for applying to the control grids of said tubes a direct current component of biasing potential of such value that substantially no anode current flows therein in the absence of the application of other components of potential to thecontrol grids of said tubes, means for applying components of potential from said source of alternating current potential to the control grids of said tubes in phase, means for applying components of potential sub-harmonically related to the alternating current potential derived from said source to the control grids of said tubes in phase opposition, means for adjusting the magnitude of the potentials applied to the control grids of said tubes so that said applied components'of potential of the lower frequency are at least as great in amplitude as the components of potential of the higher frequency, and means for adjusting the phasal relationship between said applied potentials.

10. A wave transmission system in accordance with claim 9 including means for modulating the waves translated by each of said tubes in accordance with separate individual signals.

trol electrodes of said tubes so that only one of said tubes may pass anode current at any instant, means for separately modulating the oscillations translated by the two tubes of said pair, and means for combining and transmitting the separately modulated oscillations.

12. A radio transmission system for modulating a carrier wave of frequency 2 with two intelligences, comprising a source of oscillations, means for deriving from said oscillations two potentials, one of frequency f and one of frequency 2 means for rectifying the potential of frequency f, a pair of radio frequency translators of the thermionic tube type, each having at least a cathode, a control grid and an anode, means I for applying to the control grids of said tubes a 11. A radio transmission system for modulating alternate groups of cycles of a carrier wave of frequency 211.), with two separate intelligences wherein 'n is any integer, comprising a source of oscillations, means for deriving from said source of oscillations, oscillations of two frequencies, one of frequency f and one of frequency 2n), a pair of radio frequency translators of the thermionic tube type each having at least a cathode, a control electrode and an anode, means for applying to the control electrodes of said tubes a component of biasing potential of such value that substantially no anode current flows in said tubes in the absence of the application of other components of potentials thereto, means for impressing upon the control electrodes of the tubes of said translators potentials of frequency f in phase opposition, means for impressing upon the control electrodes of the tubes of said translators other potentials of frequency 211.1, means for adjusting the phase and amplitude of the potentials of said two frequencies impressed upon the con steady direct current component of biasing potential, of such value that substantially no anode current fiows therein in the absence of the application of other components of potential to the control grids of said tubes, means for impressing upon the control grids of the tubes of said translators a potential of frequency 2) in phase in the two tubes, means for impressing a. rectified component of potential of frequency 1 upon the control grid of one of said tubes, means for impressing another rectified component of potential of frequency upon the control grid of the other of said translator tubes alternately, the

said rectified components of potential being at least as great in amplitude as the components of potential of frequency 2] and of the same polarity as the direct current component of biasing potential means for separately modulating the oscillations delivered to the two translators of the said pair and means for combining and transmitting the separately modulated oscillations.

13. A system in accordance with claim 12, in which the rectified portions of the potential of frequency f are impressed upon the individual translator tubes by way of non-inductive resistances in the grid circuits of said amplifiers.

14. A system in accordance with claim 2 in which the component of potential of frequency ,f impressed upon the control electrodes of said amplifiers is pulsating and uni-directional in character and of the same polarity as the direct current component of potential applied thereto.

15. A wave translating system for dividing an alternating potential of frequency f into groups of cycles including at least one cycle per group comprising in combination at least one pair of thermionic tubes each having at least a cathode, a control grid and an anode, means for applying a direct current component of biasing potential to the control grids of said tubes, means for exciting the control grids of said tubes in phase by said alternating potential of frequency 1, means for securing a second alternating potential sub-harmonically related to said first-mentioned potential, means for separately rectifying both halfwaves of said sub-harmonic potential, means for applying the rectified half-Wave components of potential to the respective grids of said tubes so as to aid the direct current component of biasing potential applied thereto, whereby the tubes of said pair are rendered inoperative in alternate order effecting a translation'of the potential of frequency f first by one of said tubes and then by the other.

16. A system in accordance with claim 15 including means for separately modulating with different signal intelligencies the potentials of,

frequency f translated by said tubes.

MAURY I. HULL. 

